In digital broadcasting systems, video and voice signals are compressed by MPEG (Moving Picture Experts Group) compression encoding technique, for example, and a multiplexed transport stream (TS) is digitally modulated and transmitted as a digital modulation signal. On a receiver side, the received digital modulation signal is demodulated to generate a transport stream, which is divided and analyzed into video, voice, and other information. Thus, a video image such as a program is indicated on a display.
FIG. 4 shows a structure of a radio video transmission/reception system in a digital broadcasting system. Each of a video signal and a voice signal output from a DVD 30 and a VTR 32 is input to an NTSC encoder 11 and an audio analog-to-digital converter 36 where an analog signal is converted into a digital signal. The resultant digital signals are then input to a codec 38 where the digital signals are subjected to predetermined processing such as compression processing, and output as a transport stream. The transport stream is then modulated in a radio transmission section 40 and is output as a radio signal.
Meanwhile, the transmitted radio signal which is received by a radio reception section 42 of a radio video reception device. The received radio signal is input to a codec 44 where the input radio signal is subjected to expansion (decompression) processing, which is an inverse process of that applied by the codec 38, to thereby obtain a video signal and a voice signal. The video signal and the voice signal are further input to an NTSC decoder 46 and an audio digital-to-analog converter 48, respectively. The NTSC decoder 46 and the audio digital-to-analog converter 48 apply digital-to-analog conversion to the video signal and the voice signal to generate respective analog signals, which are then output to a display 50. In this manner, a video signal which is radio-transmitted can be displayed on the display 50.
Here, in order to achieve clock synchronization between the transmission side and the reception side of such a digital broadcasting system, the codec 38 and the codec 44 multiplex the transport stream with PCR (program clock reference).
More specifically, on the transmission side, PCR data are inserted for each packet of decoding and reproduction called an access unit. Meanwhile, on the reception side, the portion in which the PCR data are inserted is detected on the basis of description of a PMT (program map table) so that an STC (system time clock) can be extracted from the PCR data, and the STC is then supplied to a clock reproduction section. The clock reproduction section includes a voltage controlled oscillator (27 MHz, free-running), a counter, or the like, thereby forming a PLL (phase locked loop) circuit, and adjusts the timing for reproducing a video signal on the basis of the clock period represented by a value of the counter and the value of STC which is received (see Japanese Patent Laid-Open Publication No. 2003-8932).
Recently, there has been proposed a reception system including a main body reception device (a main television device) which receives digital broadcast and a slave television device which receives and displays video and voice data which are radio-transmitted from the main body reception device. In such a reception system, as in the digital broadcasting system described above, a transport stream is subjected to digital modulation and transmitted, and the transport stream is multiplexed with PCR so as to achieve clock synchronization.
However, use of PCR for the purpose of achieving clock synchronization, as described above, raises a problem that the scale of a radio transmission circuit is increased.
In view of the above circumstances, the present invention advantageously provides a radio video transmission device, a radio video reception device, a radio video transmission/reception device, a signal generation device, a signal decoding device, and a signal generation/decoding device, capable of clock synchronization of video between transmission and reception sides with a simple circuit structure.